Mechanical impedance measurements for improved cost effective process monitoring

The aerospace industry has seen a considerable growth in composite usage over the past ten years, especially with the development of cost effective manufacturing techniques such as Resin Transfer Moulding (RTM) and Resin Infusion under Flexible Tooling (RIFT). The relatively high cost of raw material and conservative processing schedules has limited their growth further in non-aerospace technologies. In-situ process monitoring has been explored for some time as a means to improving the cost efficiency of manufacturing with dielectric spectroscopy and optical fibre sensors being the two primary techniques developed to date. A new emerging technique is discussed here making use of piezoelectric wafers with the ability to sense not only aspects of resin flow but also to detect the change in properties of the resin as it cures. Experimental investigations to date have shown a correlation between mechanical impedance measurements and the mechanical properties of cured epoxy systems with potential for full process monitoring.